This invention relates to a valve actuating structure for operating poppet valves and more particularly to the rotation prevention structure of a valve lifter for an internal combustion engine.
A wide variety of reciprocating machines such an internal combustion engines employ poppet valves that are operated through camshafts via followers in the form of valve lifters such as thimble tappets. These valve lifters are supported for reciprocation in bores formed in an engine body and are operatively interposed between the cam lobes the valve stems.
Conventionally, the valve lifters or tappets are formed as cylindrical bodies having an upper surface engaged by the cam and which has a shape of the arc of a circle when viewed in the direction of the camshaft axis. In a perpendicular plane, the upper surface has a generally linear configuration. Thus, the top surface of the valve lifter engaged by the cam lobe is in the form of a section of a cylinder. However, because of this construction, there is likelihood that the operation of the lifter by the rotation of the cam can also cause rotary motion of the lifter about its reciprocal axis. This can result in undue wear of the lifter and/or receiving body of the engine, which can be detrimental to optimum performance.
It is, therefore, a principal object to this invention to provide an improved structure that serves the function of preventing rotation of the valve lifter upon operation of the valve and due to rotation of the actuating cam.
It is important when considering the valve timing of an engine to minimize the reciprocating masses. As the reciprocating masses increase, the inertia on the entire system increases resulting in the possibility of valve flow and decrease performance. It is, therefore, a still further object to this invention to provide an improved arrangement for precluding rotation of the valve lifter upon its actuation and which is done in a way so as to avoid any increase in the mass of the valve lifter.
This invention is adapted to be embodied in a valve lifter arrangement for operating a poppet valve from the rotating can of a camshaft. The construction comprises an engine body defining a cylindrical bore. A valve tappet having a generally cylindrical body portion is supported for reciprocation in the cylindrical bore. The valve tappet has a head portion adapted to be operated by the cam. In accordance with the invention interengaging portions carried by the valve tappet and the engine body permit reciprocation of the valve tappet in the engine body but prevent rotation thereof.